Columbia Sportswear Omni-Heat&reg; Base Layer Top - Midweight 85% polyester, 15% spandex Omni-Heat thermal reflective system reflects and retains body heat for an average of 20% more warmth Omni-Wick advanced evaporation technology moves and disperses sweat away from the body for rapid evaporation Ergonomic flatlock seams Midweight base layer Long sleeves